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Bachelors Theses and Reports, 1928 - 1970 Student Scholarship

5-7-1938

Alkali Leaching of Antimony Sulphide andElectrolytic Recovery of Antimony from theResulting Leach SolutionVincent J. Andrews

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Recommended CitationAndrews, Vincent J., "Alkali Leaching of Antimony Sulphide and Electrolytic Recovery of Antimony from the Resulting LeachSolution" (1938). Bachelors Theses and Reports, 1928 - 1970. Paper 79.

ALY ALI LEA CHING OF ANT TIffONY SULPHIDl!!

AND

E:.ECTROLYLIC Rli:COVERY OF ANTI~JIONY

FROM THE

RESUTTING LEACH SOLUTION

by

Vinoent J. Andrews

A ThesisSubmitted to the Department of Metallurgy

in Pertial Fulfillment ofthe Requirements for the Degree of

B~ohelor of Scienoe in Metallurgical l!1ngineering

l'iontanaSchool of Hi neaButte, l."ontanaMay 7, 1938

ALKALI LEACHING OF ANTIMONY SULPHIDEAND

EI,ECTROLYLIC RECOVERY OF ANTIMONY}"'ROMTHE

RESULTING LEACH SOLUTION

byVincent J. Andrews

A ThesisSubmitted to the Department of Metallurgy

in Partial Fulfillment ofthe Requirements for the Degree of

Bachelor of Soience in Metallurgical Engineering

Montana Sohool of MinesButte, MontanaMay 7, 19;:38

17959

r-M--

TABLE OF CONTENTS

Items

Introduction • • , • • • • • • • • • t I • • • • • • • • • • I • • • • • • • • • • •

llOXperimentalEffeot of Ooncentration on Extraction •••••• 4

• • • • • • • • • t • • • • • • • • • • • • • • • • • • • • • • t • • •

Concentration & Extraction Table. • •• •• •••• • •Ooncentration & Extraotion Curves •• • •• • •• ••

Effeot of Leaohing Time on Extraotion •••••• 9Time--Extraction Table • • •••• •• • • • • • • • •• ••• •Time--Bxtraction Curve • • • I • • • • • • • • • • • • • • • • •

Effeot of Temperature on Extraction •••••••• 12Temperature--Extraotion Curve •• ••• •• •• • • • ••Temperature--Extractlon TableEffect of the Amount of Stibnite Used

• • • ••• • ••• • • • •

••••• •

Amount--Extraction Table •• • •• • • • • ••• ••• • • ••Amount--Extraction Curve • • • • • • • • • • • • • •• • •• •

Effect of Roasting • • • • • • • • • • • I • • • • • • • • • • • • •

Eleotrolysis • • • • •• • ••• • • ••• • • • • • ••••••• ••• •Current Density--Current Efficiency Table •• a9

SUl1l.DlS ry ..... ....•..•• 41 • 4t • • • • • • • • • • • • • • • • • • • • • • •• 2D

page

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INTRODUCTION

Stlbnite (5b2 S3), antimony sulphide or glanoe, isthe chief mineral from which antimony is extracted. Up

to the present time dry methods have been generallyadopted for the extraction of antimony from Stibnite.The wet and electrolytic methods have received muchattention in Europe and Ameriaa, but have yet found nopractical applications.

There have been several proposals for the extractionof antimony from its ores electrolytically. Borohes0proposed a method using a sodium sulphide solution asthe solvent for Stibnite to form a solution of sul-phantimonite and sulphantimonate and electrolyzing thesolution by the use of inSoluble anodes.

2Koepp leached the Stibnit~ with a solution offerric ohloride according to the equation:

6 FeOla'" Sb2S3 .:6F,e012 + 2 SbC13-r 3Sand electro1yed the solution at 500 C., using leadelectrodes.

Siemens and Halske3 extracted antinomy from Stib-nite with alkali sulphides, hydrosulphides, or poly-sulphides. The Stibnite was brought into solution inthe form of a double salt that is with NaHS

........~..................................................................1. Eleotro ...Meta11urgie p. 148 Brauanschweig 18912. Handbook of Metallurgy Vol. 2 by Sohnabel3. German patent, No. 67, 973 June 29, 1892

-2...

The liquor was then eleotrolyzed in diaphragm chamberswith carbon or platinum anodes and oopper or antimonycathodes. Siemens also used alkaline earth sulphidesas the solvent. No practioal applioations appear tohave been made of these prooesses.

D. J. Demorestl made some experiments on a smallscale at Ohio state University using an 8% sodiumhydrexide solution as the eleotrolyte. The antimonywas deposited on 12 x 12 inoh oathodes suspended ina tank 60 x 18 x 18 inohes using a ourrent density of7 amperes per square foot at 2.7 volts.

The drawbacks to the process were the oompara-tively low solubility of antimony in the electrolyteand the accumulation of the sulphur in the solutionwhich decreased the solvent power of the solution anddestroyed the iron anodes.

As a result of these experiments a plant wasbuilt on a large scale oapable of treating 600 poundsof antimony per day at a ourrent effioienoy of 76%.The eleotrolyte was regenerated or renewed when theanodes were attacked. No great oommeroial successappears to have favored the enterprise.

• • • • • • • • • • • • 4 • • • • ~ • • 4 ~ • 4 e • • 4 ••• ~ c • 4 • • • • • • ~ • e 4 • • ~ 0 c ~ ~ ~ ~ •

1. Journal of American Institute of Metal, Vol. XI, No.1

(

The electrolytio method of extracting antimony isohiefly desired for treating low grade antimony ores and·residues where other methods cannot be used economically.

It is the purpose of this investigation to obtainsome insight into optimum oonditions for leaching Stib-nita with sodium hydroxide solution and also to steudythe fectors affeoting the eleotrolysis of the resultingsolution.

,.

EXPEHIMENTAL

To study the effeots of oonoentration of solution,time of leaohing, temperature of leaohing, amount ofsolute, and the roasting of Stibnite before leachingon the extraotion of antimony from Stibnlte by leaoh-ing)the following experiments were performed. TheStibnite used in the experiments was purohased fromthe Merk Chemioal Company and oontained a small a.mountof arsenio. The leaohing solution was mad~ by dis-solving the required amo~t Qf stiok sodium hydroxidein the required amount of distill water.

The Effeot of ConcentrationThe leaohingexperiments were oarried out in 400

8 e beakers. A four gram sample of stibnite wasweighed out and plaoed in the beaker with 250 8 & ofsodium hydrOxide solution. The conoentration ofsodium hydroxide solution used consisted of 15, 30,60, and 120 grams per 1,000 c 0 of water. The oontentsot the beaker were stirred frequently with a stirringrod. The temperature was kept constant. At the endof a half-hour1the mixture was immediately filteredthrough a laboratory vaouum filter and 2-25 c 0 portionsof the filtrate were pipetted and analyzed for antimony,

-5-

Using Low'sl permangnate method. Knowing the eriglnal.:

volume of the solute and amount of Stibnite used,theperoentage extraotion is easily oaloulated.

The reaotion whioh takes plaoe during the solutionof etibnite in sodium hydroxide is:

Sb2Sa + 2NaOH -= NaSbS2 +NaSbSQ t- H20aooording to D. J. 'Demore~tl and others.

The results obtained are shown tabulated in table 1.and graphioally represent~a in figures 1,2, & 3. Alldeterminations were done in duplioate and the ~verage ofthe results ta~en.Table l.--The Effeot of Conoentration on Extraction

Time of leaohing t hour l,~our 2 hourstemperature 20° C.Quantity of stibnite used 4 gramsQuantity of solution 250 0 0

Variable oonoentrationConoentration of NaOHin grams per liter t hour

ExtractionLeaohing Time

1 hour 2 hours153060

120

1. Teohnical Methods of Ore Analysis by Low2. The Journal of Amerloa~ Inlsitute of Metals, Vol.Xl,No.l

-6-

100

90

80,.,

70

600

50~t 40~"--i, 300

I:)

~-c,'>< 20lu

10

30 60 90 120Ooncentration - grams Na OR/liter

Fig. I - Effeot of 60ncentration on ExtraotionTime of leaohing t hour,Temperature 20° o.Quantity of stibnite used 4 gramsQuantity of solution 250 C 0Variable concentration

•

100

-7-

90

80G70

60

~ 50~<;)

""\.._ 40~~--N 30~l!J

20

10

30 60 90 120Concentration - grams NaOll/liter

Fig. II - Effect of Concentration on ExtractionTime of leaching 1 hourTemperature 200 c.uantity of s~ibnite used 4 grams

Quantity of solution 250 C CVariable concentration

..8 ..

100

- r90

80

070

60

'"~ 50t::<;)<, 40-4-..~I:)

~-w 30~Ul

20

10

90 120

Concentration - grams Na Oll/liter

Fig. III - Effect of Concentration on ExtractionTime of leaching 2 hoursTemperature 200 C.Quantity of Stibnite used 4 gramsQuantity of solution 250 C CVariable concentration

-9 ..

From the plotted results, it is readily seen that themaximum extraction is obtained with a concentration of60 grams per liter. using higher ooncentrations tha~60 grams has no effect on extraction and weaker con-centrations lower the extraction •

.Therefore the effect of time on extraction wasdetermined for there solutions.

Effeot of Leaohing TimeIn determining the effeot of time on extraction

similiar procedure was followed as in the preoedingdeterminations. In this oase, however, time was thevariable. The conoentration'and temperature were keptconstant for eaoh sat of determinations.

Results are given in table II and illustratedgraphioally in figures 3 and 4.Table II.':'-The.Effect of Time on Extraction.

Concentration of solvent 60 and 120 grm/ literTemperature 200Quantity Stibnite used 4 gramsQuantity of solution 250 c cVariable timeTime in Per Oent Extraotion

Con. of leaohing solution60gms. /"liter 120 gms / literMinutes

163060120.,

~10..

1

."" .

10

90

80

70

60

~ 50t::<;)., 40~\)

~4.."\-l 30~11l•• 2

30 60 90 120

Time in MinutesFig. IV - Effect of Time on Extraction

Concentration of solvent--60 grams / liter~emperature--20oC.~uantity·of Stibnite used 4 grams~uantity of solution 250 c cVariable time

-11..

100

900

80

70 G 0

60~

t:: 50~

"

" 40~ -~-l.-N 30~kJ

30 60 90 120

Time in ].inutesFig. V - Effect of Time on Extraction

Concentration of solvent--120 grams / literTemperature--20oC •.Quantity'of Stibnite used 4 grams~uantity of solution 250 c cVa riable time

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It is apparent from the ourves and table that timehas no marked effeot on the extraotion.

The Effeot of TemperatureThe prooedure in obtaining these results was again

similar to the previous determinations. The leaohing at00 C. was done by immersing the beaker oonta.ining thesodium hydroxide solution in a freezing mixture of snowand salt until the solution beoame the same temperaturea.sthe bath when the Stibnite was introduced. The 100 c.leaoh was done in a similar manner except inst~ad ofusing snow and salt, tap water was used whose temperaturewas 100 C. The 400 C" leach was aocomplished in a Freaswater thermostat. The leaoh at 960 C. was performed byheating the leaoh solution to boiling on a hot plate.The solution ,was kept oovered with a watoh glass to pre-vent excessive evaporation. When the solution boiled,the Stibnite was introduced cautiously and allowed toboil several minutes. It was then immediately filteredand same prooedure followed as in the previous experi-ments.

The results obtained are shown in table 3, andrepresented graphically in figure 6.

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100

90,

80,

70.

60.'<;:)

~ 50.t<:>

._;:40,~\::J-l....

'1..... 30.~LU 0

20

10-

20 40 60 80 100

Tempera ture in Degrees CentigradeFig. VI - Effect of Temperature on Extract'on

Concentration of solvent--60 grams / literTime of ~eaching t hourQuantity of Stibnite used 4 grams~uantity of solution 250 c cVariable temperature

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Table IV.--The Effect of the Amount of Stibnite Placedin Solvent.Conoentration of solvent 60 grams / literTime of leaching 1 hourTemperature 200 C.Quantity of solution 250 0 0

Variable amount of Stibnite used

Amount of'Stibnite Percentage Grams of Sb perused Extracted Liter of Solution1 75~ 2.102 73% 4.103 70% 5.954 71% 8.358 37% 8.60

From the results obtained it is apparent that themore Stibnite there is introduced into the solutionthe greater is the amount that goes into the solutionup to a oertain pOint. This is the prinoiple of thelaw of mass action which holds until the solution be-comes saturated with antimony. In this oase thesolution is saturated with antimony when it oontains8.6 grams per liter.

It is apparent that the high extractions obtainedin the preceding determinations are misleading sincesmall amounts of Stibnite were used. It should benoted that the amount of antimony that NaOH will holdin solution is limited and very small.

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Table III.--The Effeot of Temperature on .l:!;Xtraction.Concentration of Solvent 60 grams / literTime of leaching t hourQuantity of Stibnite used 4 gramsQuantlty of solution 250 c 0

Variable Temperature

Temperature Per Cent ot

Degrees Centigrade Extractiono

10204097

The examination of the table and curves reveal thattemperatures above 200 C. have no marked effect on theextraotion.

Effeot of the Amount of Stibnite usedSimilar procedure was oarried as in the preceding

experiments. All factors were kept oonstant exoept theamount of Stibnite introduoed into the solution. Theamount of Stibnite used per 250 0 c of solvent ~a~ 1, 2,:3,4, and 8 grams.

The results obtained are shown in table 4 andfigure 7.

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i ,100

90

800

70

60

~

~50

•. <:)<,

'" 40'<:J~~-\-J 30-~lJ.1

20•

10

2 4 6 8 10Amount of Stibnite in Grams

Fig. VII-- Effect of Amount of Stibnite on Extra:ctionConcentration of solvent--60 grams / literTime of leaching 1 hourTemperature--200C.'c:t!.uant·ity of solution 250 c cVariable quantity of Stibnite used

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~IU 10~<,

~'-1~\)-.\.. 8~

~~<:;)

~ r...... U'i-.t:~

'\.4...~

"'i-.... 4~~<;:)

t~

6 8 10

Amount of Stibnite in GramsFig. VIII -'Amount of antimony grams / liter

Concentration of solvent--60 grams / literTime of leaching 1 hourTemperature--20 C.Quantity of solution 250 c cVariable quarrt i t y of Stibnite used

,

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Effeot of RoastingT The roasting of the Stibnite was done in smallroasting dishes in a gas muffle furnace. Ten gramsof Stibnite were weighed out, placed in eao~ of foursmall roasting dishes and roasted in the furnace withoontinous rabbling and a plentiful supply of air.The temperatures of roasting were 3400 C. and 4000

IC. A small dish .of the roasted Stibnite was takenfrom the furnace at fifteen minute intervals.

Table V.--The Effeot of Roasting on Extraction'I

Conoentration of Solvent 60 gramsTime of leaohing t hourTemperature 200 C.Quality of Roasted Ore 4 gramsQuality of Solvent 250 c 0

Time of Roasting Antimony in grams / literin Minutes Temperature of Roasting

350 40015 .230 .4 .245 .4 .260 .7 .2

Pure Sb20 .7

In order to determine the effect of roasting onextraction, the roasted sulphide was leached with NaOH.

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The leaching was done as in preceding deter-mination. The results obtained are shown in table 5.

From table 5, it is readily seen that the roast-ing of the ore does not aid in increasing the amountof antimony in solution.

ElectrolysisA few electrolyzing experiments were carried out

to determine the effect of current density on characterof deposit and current efficiency. For this purpose asolution obtained from leaohing Stibnite with 60 gramsof NaOR / liter was used. It contained 8.6 grams ofSb / liter. The electrolyzing was done in a 250 0 0

beaker using lead anode and oathode at an E. H. F. of2.75 volts and various ourrent densities.

The results obtained are given in table 6.Table VI.--The Effect of Current Density on Nature at

IDeposit and Current Efficiency.

C. D. in 1mps , Current Nature of/ Sq. Ft. Efficienoy Deposit

9 77%16 84% black not22 79% very28 58% coherent33 79$'0

LIt;C.~•• TA..~A SCHOO ... Of lV"dNESL.lli IV-}

BUTTE

From table VI the current efficiency does notshow any relationship to the current density. Thisis probably d:ue to the faQt that the incoher~nt depositof antimony fell off from the .cathodes duri~g elec-trolysis giving the erratic results for currentefficiency.

The Electrolyte did not seem to affect the leadelectrodes. The surface of the anode became coatedwith Pb02 apparently which protects the. lead fromattack of the electrolyte.

17959

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SUMMARY

1. Antimony sulphide is leached with sodiumhydroxide using various solvent concentrations,leaohing time, and temperature. The maximum 'solubility of antimony in sodium hydroxide is 8.60grams of antimony per liter of 6% NaOR solution atroom temperature.

2. Temperature changes above room temperature donot appreoiably affect the solubility.

3. Time of leaching has no affect on theextraction.

4. Roasting of the Stibnite previous to theleaching deoreases the extraction and the amount ofantimony in solution.

5. The antimony from the leach solution oan beprecipated with an eleotric current using leadelectrodes at a current efficienoy ot" approximateiy'

".

ACKNOWLEDGEMENTS

I wish to acknowledge my indebtedness toDr. Ourtis L. Wilson, Professor of Metallurgy,Montana School of Mines, and to Dr. Ettore A.Peretti, Instructor of Metallurgy, MontanaSchool of Mines, for their advise and helpfuls~~gestions during the progress of myresearch; also to Prof. L. J. Hartzell,Professor of Chemistry, Montana School ofMines, for his assistances and advise in theanalytic work.